In order to meet the very stringent requirements on exhaust particulate emissions being imposed by governmental regulators, modifications to the engine and/or exhaust treatment strategies are necessary. Although particle traps are known in the art, many employ cordierite as the filter medium, and use some separate regenerator, such as injected fuel or an electrically resistive heater, to regenerate the filter. Although several filter mediums are known in the art that can effectively capture particulate matter in a wide range of particle sizes suitable for treatment of an engine's exhaust, efficiently regenerating the particle traps has been much more problematic. For instance, regenerating particle traps by burning fuel in the exhaust section to create the heat necessary to cause regeneration (i.e. burn the particulate matter) can result in an excess usage of fuel, cause uneven regeneration of the filter medium and potentially create even further undesirable emissions. Likewise, particulate trap strategies that employ an electrically resistive heater embedded in, or positioned adjacent, a filter medium can also experience uneven regenerative heating and can consume relatively large amounts of electrical power to perform the regenerative function.
Existing systems often suffer from additional energy consumption due to the fact that regenerative heaters must heat the filter medium well above typical exhaust temperatures. When regeneration is performed with the engine running, the exhaust flow blowing over the filter medium tends to cool the same. Thus, even larger amounts of heat energy must be supplied to overcome this continuous cooling of the filter medium that occurs due to exhaust gas flow. In addition, many prior assemblies attempt to regenerate almost the entire particulate filter assembly in a single operation, which can also place large energy demands on an engine's electrical system.
The present invention is directed to one or more of the problems set forth above.